Heating, ventilating, and air-conditioning (HVAC) systems have been used to ventilate and maintain desirable temperatures within spaces such as buildings, and other at-least partially enclosed spaces have been equipped with ventilation systems including HVAC systems to provide comfortable and safe environments for occupants to live and work, for example. HVAC equipment and units such as air handlers, air conditioning units, heat pumps, furnaces, and the like have been mass produced in a variety of sizes and configurations, and appropriate sizes have been selected to be installed in various buildings having different or unique HVAC ductwork.
Many prior art HVAC units have had single speed blowers designed to provide adequate flow for typical ductwork. However, different buildings with different ductwork have had varying amounts of airflow restriction, and prior art HVAC units installed in such systems have often provided too much or too little flow in installations where the ductwork provided more or less airflow restriction than the HVAC designers had anticipated. In installations where airflow restriction significantly exceeded what the designers had anticipated, actual airflow rates have been insufficient, resulting in reduced energy efficiency as a result of reduced transfer of heat, inadequate heating or cooling of the space, higher utility bills than expected, frost formation on evaporator coils, or a combination thereof, as examples. On the other hand, in installations where airflow restriction has been significantly less than what the designers anticipated, HVAC units have produced more noise than desired, consumed more fan energy than necessary, provided excessive airflow to the space causing excessive air movement within the space, or a combination thereof, as further examples.
Further, certain HVAC units have been used that have had variable speed fans or blowers. Some such systems have been used in variable air volume (VAV) systems, for example, and have used variable speed drive units, such as variable frequency AC drive units and variable voltage DC systems. In some specialized installations, variable-speed fans have been used to compensate for variations in airflow restriction in HVAC ductwork. However, this has typically required the attention of skilled personnel who have measured airflow rates using handheld instruments such as Pitot tubes, measured airflow rates at registers, performed calculations, or a combination thereof, for example. In many installations, technicians of the necessary skill level are not available for this purpose or would add too much cost to the expense of installing and commissioning an HVAC unit. Further, prior art systems that provided for compensating for variations in airflow restriction within HVAC ductwork typically required specialized measurement equipment for measuring airflow rates directly, for example, which added cost and complexity to HVAC systems and, at least in some cases, reduced reliability of HVAC systems. Further, prior art systems did not operate continuously and therefore did not compensate for changes in airflow restriction that occurred after the system was commissioned, such as partial clogging of filters, user adjustment of registers, and modifications to the ductwork, as examples.
Accordingly, needs and potential for benefit exist for HVAC equipment, systems, and methods that provide for some degree of compensation for variations in ductwork restriction in different installations. In addition, needs and potential for benefit exist for such equipment, systems, and methods that at least partially compensate for changes in airflow restriction that occurred after the system was commissioned, such as partial clogging of filters, user adjustment of registers, and modifications to the ductwork, as examples. Further, needs and potential for benefit exist for such equipment, systems, and methods that are inexpensive, utilize existing components (e.g., to a greater degree), are reliable, and are easy to place into service by typical installation personnel. Further still, needs and potential for benefit exist for such equipment, systems, and methods that maintain (at least to some extent) cooling or heating effectiveness (or both) over a range of varying ductwork airflow restriction, that provide for reduced energy consumption, that provide for reduced noise, that avoid frost formation on evaporator coils, that avoid insufficient or excessive airflow rates, or a combination thereof, as examples. Needs and potential for benefit exist for such equipment, systems, and methods in typical residential applications, for example, such as mass-produced residential air-conditioning units, heat pumps, furnaces, and the like, that are suitable to be installed by typical installers of such equipment. Potential for improvement exists in these and other areas that may be apparent to a person of skill in the art having studied this document.